When a boat electric system is plugged into a shore power system, a galvanic isolator is often positioned in series with the connection between shore ground and boat ground. The galvanic isolator prevents the flow of destructive galvanic currents, while maintaining the safety of function of a neutral ground by conducting when the difference of potential between the two grounds exceeds a preset amount. The isolator generally is made to block current when the potential difference is below about 1.4 volts, and conduct above that value. U.S. Pat. No. 5,840,164 issued Nov. 24, 1998 to Staerzl discusses the problems encountered with heat dissipation when large currents flow through the ground circuit. The isolators of the prior art are large, expensive, and difficult to mount with adequate ventilation in the confines of some boats. Consequently, they are often omitted. This can lead to dangerous corrosion, fire, and shock hazards.